Yes and yes. Mixing would go in the same way, except the uv coordinates. The first input of the addition would be the triplanar normals, and the second is the decal normals.
This isn't an actual texture for anything its just a slate im practicing on. The top and the bottom are both the same except the top has crappy fake lighting.
im using a xbox360 controller with psx analog sticks (harvested from old malfunctioning dualshock) except for the digital pad its the best controller out there